We do not know why some women who give birth vaginally sustain an extensive major levator ani (LA) muscle tear. Nor do we know why 1 in 10 women suffer pelvic organ prolapse. In 2003, we began testing thishypothesis in a sample of women predisposed for LA injury because all had obstetric events associated with LA trauma (e.g. forceps, anal sphincter tear). With these high risk women, the tear was still only partial, less than 50% muscle fiber loss. Since it is major LA tear that is associated with prolapse when studied in multipara later in life, we need to learn about LA tear progression from first to second birth and how this contributes to prolapse later in life. We hypothesize that 1) exposure again to vaginal birth after an initial LA partial tear places a woman at high risk for more extensive LA tear, that 2) extension in LA tear is associated with increased pelvic organ descent, and this is because 3) the LA becomes unsupportive when it is no longer tethered to its origin. We aim to test these hypotheses in a highly efficient prospective cohort design. About 45% of our previously established cohort of first-birth women showed partial LA tear when evaluated by MRI. and the other half exhibited no evidence of tear despite also having obstetric risk factors for LA tear on first birth. We will study all of the women again to detennine if partial tear determines higher risk for extensive injury and increased prolapse when they birth again. All of the women in this established cohort have consented to further contact. We plan to evaluate those who have given birth vaginally a second time, comparing MRI data post first birth versus post second birth to quantify change in LA tear status, change in descent of the pelvic organs, and the relationship between the two. The degree of LA tear will be measured using the redesigned and novel instrumented speculum that eliminates crosstalk from intra-abdominal pressure during volitional contraction. Organ descent will be measured by comparing common organ position in both subject MRIs. This project has high impact through three independent pathways to clinical relevance. It will: 1) close the time-gap between the initial injury (first birth) and later life pronounced prolapse symptoms by demonstrating that injury extension and symptom progression are predicted by partial tear at first birth, 2) begin to shift the current paradigm of elective Cesarean for all to prevent LA injury to data-based selection criteria, and 3) pave the way for new interventions targeted to those women most at risk, those who give birth again after an initial partial LA tear on first birth.